The invention provides a thermoelectric conversion material having a low thermal conductivity and an improved figure of merit and a production method for the material, and also provides a thermoelectric conversion module. The thermoelectric conversion material has, on a porous substrate having microscopic pores, a thermoelectric semiconductor layer formed of a thermoelectric semiconductor material, wherein the porous substrate has a polymer layer (B) on a plastic film (A) and the microscopic pores are formed in the polymer layer (B) and in a part of the plastic film (A). The production method for the thermoelectric conversion material comprises a substrate formation step of forming a porous substrate including a step 1, a step 2 and a step 3, and comprises a film formation step of forming a thermoelectric semiconductor layer through film formation of a thermoelectric semiconductor material on the porous substrate. The thermoelectric conversion module uses the thermoelectric conversion material.